Elevators move people and objects vertically along a track, for example between floors or platforms of a building or other structure. Traction elevators are suspended and moved by traction cables driven by a motor. The traction cables may, for example, be steel ropes which are pulled over a grooved pulley system called a sheave or may be flat belts made of steel or polyethylene. Hydraulic elevators are suspended and moved by a piston that is moved through a hydraulic cylinder by means of a pump. One or more guide rails may define the track that an elevator car moves along between the upper terminus and the lower terminus of the track.